The overall goal of this research program is to investigate the role of parent behavior on the development of repetitive arm, hand, and finger movements in young infants-gestures that have recently been studied as an analog to infant vocal babble. Specifically, this project will investigate the responsiveness of parents to these repetitive infant gestures and will experimentally test the role of parental reinforcement on their production over time. Taking a Dynamic Systems approach, the overall hypothesis is that children are born with innate predispositions to produce behaviors that appear to adults as very speech- or sign-like- repetitive vocalizations and gestures, respectively. As children mature, they have an expanding "pool' of motor behaviors that may be used in various contexts. In contexts where these behaviors are functional (e.g. parents respond to and reinforce them), they are maintained and continue to pull from the available pool. In contexts where they are not functional, they do not change and eventually drop out. The present project will consist of two longitudinal small-sample studies and one large-sample study of adult responsiveness to repetitive infant gestures. In Study 1 of the present project, the responses of hearing parents to repetitive gestures produced by their hearing infants from 6 to 12 months of age will be studied and compared to those of deaf, American Sign Language (ASL)-signing parents of deaf infants. These data will provide information about the natural responses of parents, both hearing and deaf, to repetitive babble-like gestures produced by young infants. In Study 2, the ability of hearing, nonsigning adults to identify repetitive infant gestures from a "background' of ongoing infant motor activity will be assessed. These data will provide new information about the potential of hearing adults to recognize babble-like gestures in young infants. In Study 3, the effect of parent reinforcement on repetitive infant gestures will be experimentally tested by training hearing parents to provide social reinforcement for nonreferential repetitive gestures produced by their hearing infants between 6 and 16 months of age. These data will inform our models of language learning by examining the role of parent responsitivity in the development of a manual form of prelinguistic babble and provide clinically relevant information about gestural parent- child interaction-important to programs encouraging gestural communication between hearing parents and deaf children.